#    Copyright 2013 IBM Corp.
#
#    Licensed under the Apache License, Version 2.0 (the "License"); you may
#    not use this file except in compliance with the License. You may obtain
#    a copy of the License at
#
#         http://www.apache.org/licenses/LICENSE-2.0
#
#    Unless required by applicable law or agreed to in writing, software
#    distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
#    WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
#    License for the specific language governing permissions and limitations
#    under the License.

"""Handles database requests from other nova services."""

import contextlib
import copy
import functools

from oslo_config import cfg
from oslo_log import log as logging
import oslo_messaging as messaging
from oslo_utils import excutils
from oslo_utils import versionutils
import six

from nova import availability_zones
from nova.compute import instance_actions
from nova.compute import rpcapi as compute_rpcapi
from nova.compute import task_states
from nova.compute import utils as compute_utils
from nova.compute.utils import wrap_instance_event
from nova.compute import vm_states
from nova.conductor.tasks import live_migrate
from nova.conductor.tasks import migrate
from nova import context as nova_context
from nova.db import base
from nova import exception
from nova.i18n import _, _LE, _LI, _LW
from nova import image
from nova import manager
from nova import network
from nova import notifications
from nova import objects
from nova.objects import base as nova_object
from nova import profiler
from nova import rpc
from nova.scheduler import client as scheduler_client
from nova.scheduler import utils as scheduler_utils
from nova import servicegroup
from nova import utils

LOG = logging.getLogger(__name__)
CONF = cfg.CONF


def targets_cell(fn):
    """Wrap a method and automatically target the instance's cell.

    This decorates a method with signature func(self, context, instance, ...)
    and automatically targets the context with the instance's cell
    mapping. It does this by looking up the InstanceMapping.
    """
    @functools.wraps(fn)
    def wrapper(self, context, *args, **kwargs):
        instance = kwargs.get('instance') or args[0]
        try:
            im = objects.InstanceMapping.get_by_instance_uuid(
                context, instance.uuid)
        except exception.InstanceMappingNotFound:
            LOG.error(_LE('InstanceMapping not found, unable to target cell'),
                      instance=instance)
            im = None
        else:
            LOG.debug('Targeting cell %(cell)s for conductor method %(meth)s',
                      {'cell': im.cell_mapping.identity,
                       'meth': fn.__name__})
            # NOTE(danms): Target our context to the cell for the rest of
            # this request, so that none of the subsequent code needs to
            # care about it.
            nova_context.set_target_cell(context, im.cell_mapping)
        return fn(self, context, *args, **kwargs)
    return wrapper


class ConductorManager(manager.Manager):
    """Mission: Conduct things.

    The methods in the base API for nova-conductor are various proxy operations
    performed on behalf of the nova-compute service running on compute nodes.
    Compute nodes are not allowed to directly access the database, so this set
    of methods allows them to get specific work done without locally accessing
    the database.

    The nova-conductor service also exposes an API in the 'compute_task'
    namespace.  See the ComputeTaskManager class for details.
    """

    target = messaging.Target(version='3.0')

    def __init__(self, *args, **kwargs):
        super(ConductorManager, self).__init__(service_name='conductor',
                                               *args, **kwargs)
        self.compute_task_mgr = ComputeTaskManager()
        self.additional_endpoints.append(self.compute_task_mgr)

    # NOTE(hanlind): This can be removed in version 4.0 of the RPC API
    def provider_fw_rule_get_all(self, context):
        # NOTE(hanlind): Simulate an empty db result for compat reasons.
        return []

    def _object_dispatch(self, target, method, args, kwargs):
        """Dispatch a call to an object method.

        This ensures that object methods get called and any exception
        that is raised gets wrapped in an ExpectedException for forwarding
        back to the caller (without spamming the conductor logs).
        """
        try:
            # NOTE(danms): Keep the getattr inside the try block since
            # a missing method is really a client problem
            return getattr(target, method)(*args, **kwargs)
        except Exception:
            raise messaging.ExpectedException()

    def object_class_action_versions(self, context, objname, objmethod,
                                     object_versions, args, kwargs):
        objclass = nova_object.NovaObject.obj_class_from_name(
            objname, object_versions[objname])
        args = tuple([context] + list(args))
        result = self._object_dispatch(objclass, objmethod, args, kwargs)
        # NOTE(danms): The RPC layer will convert to primitives for us,
        # but in this case, we need to honor the version the client is
        # asking for, so we do it before returning here.
        # NOTE(hanlind): Do not convert older than requested objects,
        # see bug #1596119.
        if isinstance(result, nova_object.NovaObject):
            target_version = object_versions[objname]
            requested_version = versionutils.convert_version_to_tuple(
                target_version)
            actual_version = versionutils.convert_version_to_tuple(
                result.VERSION)
            do_backport = requested_version < actual_version
            other_major_version = requested_version[0] != actual_version[0]
            if do_backport or other_major_version:
                result = result.obj_to_primitive(
                    target_version=target_version,
                    version_manifest=object_versions)
        return result

    def object_action(self, context, objinst, objmethod, args, kwargs):
        """Perform an action on an object."""
        oldobj = objinst.obj_clone()
        result = self._object_dispatch(objinst, objmethod, args, kwargs)
        updates = dict()
        # NOTE(danms): Diff the object with the one passed to us and
        # generate a list of changes to forward back
        for name, field in objinst.fields.items():
            if not objinst.obj_attr_is_set(name):
                # Avoid demand-loading anything
                continue
            if (not oldobj.obj_attr_is_set(name) or
                    getattr(oldobj, name) != getattr(objinst, name)):
                updates[name] = field.to_primitive(objinst, name,
                                                   getattr(objinst, name))
        # This is safe since a field named this would conflict with the
        # method anyway
        updates['obj_what_changed'] = objinst.obj_what_changed()
        return updates, result

    def object_backport_versions(self, context, objinst, object_versions):
        target = object_versions[objinst.obj_name()]
        LOG.debug('Backporting %(obj)s to %(ver)s with versions %(manifest)s',
                  {'obj': objinst.obj_name(),
                   'ver': target,
                   'manifest': ','.join(
                       ['%s=%s' % (name, ver)
                       for name, ver in object_versions.items()])})
        return objinst.obj_to_primitive(target_version=target,
                                        version_manifest=object_versions)

    def reset(self):
        objects.Service.clear_min_version_cache()


@contextlib.contextmanager
def try_target_cell(context, cell):
    """If cell is not None call func with context.target_cell.

    This is a method to help during the transition period. Currently
    various mappings may not exist if a deployment has not migrated to
    cellsv2. If there is no mapping call the func as normal, otherwise
    call it in a target_cell context.
    """
    if cell:
        with nova_context.target_cell(context, cell) as cell_context:
            yield cell_context
    else:
        yield context


@contextlib.contextmanager
def obj_target_cell(obj, cell):
    """Run with object's context set to a specific cell"""
    with try_target_cell(obj._context, cell) as target:
        with obj.obj_alternate_context(target):
            yield target


@profiler.trace_cls("rpc")
class ComputeTaskManager(base.Base):
    """Namespace for compute methods.

    This class presents an rpc API for nova-conductor under the 'compute_task'
    namespace.  The methods here are compute operations that are invoked
    by the API service.  These methods see the operation to completion, which
    may involve coordinating activities on multiple compute nodes.
    """

    target = messaging.Target(namespace='compute_task', version='1.16')

    def __init__(self):
        super(ComputeTaskManager, self).__init__()
        self.compute_rpcapi = compute_rpcapi.ComputeAPI()
        self.image_api = image.API()
        self.network_api = network.API()
        self.servicegroup_api = servicegroup.API()
        self.scheduler_client = scheduler_client.SchedulerClient()
        self.notifier = rpc.get_notifier('compute', CONF.host)

    def reset(self):
        LOG.info(_LI('Reloading compute RPC API'))
        compute_rpcapi.LAST_VERSION = None
        self.compute_rpcapi = compute_rpcapi.ComputeAPI()

    # TODO(tdurakov): remove `live` parameter here on compute task api RPC
    # version bump to 2.x
    @messaging.expected_exceptions(
        exception.NoValidHost,
        exception.ComputeServiceUnavailable,
        exception.ComputeHostNotFound,
        exception.InvalidHypervisorType,
        exception.InvalidCPUInfo,
        exception.UnableToMigrateToSelf,
        exception.DestinationHypervisorTooOld,
        exception.InvalidLocalStorage,
        exception.InvalidSharedStorage,
        exception.HypervisorUnavailable,
        exception.InstanceInvalidState,
        exception.MigrationPreCheckError,
        exception.MigrationPreCheckClientException,
        exception.LiveMigrationWithOldNovaNotSupported,
        exception.UnsupportedPolicyException)
    @targets_cell
    @wrap_instance_event(prefix='conductor')
    def migrate_server(self, context, instance, scheduler_hint, live, rebuild,
            flavor, block_migration, disk_over_commit, reservations=None,
            clean_shutdown=True, request_spec=None):
        if instance and not isinstance(instance, nova_object.NovaObject):
            # NOTE(danms): Until v2 of the RPC API, we need to tolerate
            # old-world instance objects here
            attrs = ['metadata', 'system_metadata', 'info_cache',
                     'security_groups']
            instance = objects.Instance._from_db_object(
                context, objects.Instance(), instance,
                expected_attrs=attrs)
        # NOTE: Remove this when we drop support for v1 of the RPC API
        if flavor and not isinstance(flavor, objects.Flavor):
            # Code downstream may expect extra_specs to be populated since it
            # is receiving an object, so lookup the flavor to ensure this.
            flavor = objects.Flavor.get_by_id(context, flavor['id'])
        if live and not rebuild and not flavor:
            self._live_migrate(context, instance, scheduler_hint,
                               block_migration, disk_over_commit, request_spec)
        elif not live and not rebuild and flavor:
            instance_uuid = instance.uuid
            with compute_utils.EventReporter(context, 'cold_migrate',
                                             instance_uuid):
                self._cold_migrate(context, instance, flavor,
                                   scheduler_hint['filter_properties'],
                                   reservations, clean_shutdown, request_spec)
        else:
            raise NotImplementedError()

    def _cold_migrate(self, context, instance, flavor, filter_properties,
                      reservations, clean_shutdown, request_spec):
        image = utils.get_image_from_system_metadata(
            instance.system_metadata)

        # NOTE(sbauza): If a reschedule occurs when prep_resize(), then
        # it only provides filter_properties legacy dict back to the
        # conductor with no RequestSpec part of the payload.
        if not request_spec:
            # Make sure we hydrate a new RequestSpec object with the new flavor
            # and not the nested one from the instance
            request_spec = objects.RequestSpec.from_components(
                context, instance.uuid, image,
                flavor, instance.numa_topology, instance.pci_requests,
                filter_properties, None, instance.availability_zone)
        else:
            # NOTE(sbauza): Resizes means new flavor, so we need to update the
            # original RequestSpec object for make sure the scheduler verifies
            # the right one and not the original flavor
            request_spec.flavor = flavor

        task = self._build_cold_migrate_task(context, instance, flavor,
                                             request_spec,
                                             reservations, clean_shutdown)
        # TODO(sbauza): Provide directly the RequestSpec object once
        # _set_vm_state_and_notify() accepts it
        legacy_spec = request_spec.to_legacy_request_spec_dict()
        try:
            task.execute()
        except exception.NoValidHost as ex:
            vm_state = instance.vm_state
            if not vm_state:
                vm_state = vm_states.ACTIVE
            updates = {'vm_state': vm_state, 'task_state': None}
            self._set_vm_state_and_notify(context, instance.uuid,
                                          'migrate_server',
                                          updates, ex, legacy_spec)

            # if the flavor IDs match, it's migrate; otherwise resize
            if flavor.id == instance.instance_type_id:
                msg = _("No valid host found for cold migrate")
            else:
                msg = _("No valid host found for resize")
            raise exception.NoValidHost(reason=msg)
        except exception.UnsupportedPolicyException as ex:
            with excutils.save_and_reraise_exception():
                vm_state = instance.vm_state
                if not vm_state:
                    vm_state = vm_states.ACTIVE
                updates = {'vm_state': vm_state, 'task_state': None}
                self._set_vm_state_and_notify(context, instance.uuid,
                                              'migrate_server',
                                              updates, ex, legacy_spec)
        except Exception as ex:
            with excutils.save_and_reraise_exception():
                updates = {'vm_state': instance.vm_state,
                           'task_state': None}
                self._set_vm_state_and_notify(context, instance.uuid,
                                              'migrate_server',
                                              updates, ex, legacy_spec)
        # NOTE(sbauza): Make sure we persist the new flavor in case we had
        # a successful scheduler call if and only if nothing bad happened
        if request_spec.obj_what_changed():
            request_spec.save()

    def _set_vm_state_and_notify(self, context, instance_uuid, method, updates,
                                 ex, request_spec):
        scheduler_utils.set_vm_state_and_notify(
                context, instance_uuid, 'compute_task', method, updates,
                ex, request_spec)

    def _cleanup_allocated_networks(
            self, context, instance, requested_networks):
        try:
            # If we were told not to allocate networks let's save ourselves
            # the trouble of calling the network API.
            if not (requested_networks and requested_networks.no_allocate):
                self.network_api.deallocate_for_instance(
                    context, instance, requested_networks=requested_networks)
        except Exception:
            msg = _LE('Failed to deallocate networks')
            LOG.exception(msg, instance=instance)
            return

        instance.system_metadata['network_allocated'] = 'False'
        try:
            instance.save()
        except exception.InstanceNotFound:
            # NOTE: It's possible that we're cleaning up the networks
            # because the instance was deleted.  If that's the case then this
            # exception will be raised by instance.save()
            pass

    @wrap_instance_event(prefix='conductor')
    def live_migrate_instance(self, context, instance, scheduler_hint,
                              block_migration, disk_over_commit, request_spec):
        self._live_migrate(context, instance, scheduler_hint,
                           block_migration, disk_over_commit, request_spec)

    def _live_migrate(self, context, instance, scheduler_hint,
                      block_migration, disk_over_commit, request_spec):
        destination = scheduler_hint.get("host")

        def _set_vm_state(context, instance, ex, vm_state=None,
                          task_state=None):
            request_spec = {'instance_properties': {
                'uuid': instance.uuid, },
            }
            scheduler_utils.set_vm_state_and_notify(context,
                instance.uuid,
                'compute_task', 'migrate_server',
                dict(vm_state=vm_state,
                     task_state=task_state,
                     expected_task_state=task_states.MIGRATING,),
                ex, request_spec)

        migration = objects.Migration(context=context.elevated())
        migration.dest_compute = destination
        migration.status = 'accepted'
        migration.instance_uuid = instance.uuid
        migration.source_compute = instance.host
        migration.migration_type = 'live-migration'
        if instance.obj_attr_is_set('flavor'):
            migration.old_instance_type_id = instance.flavor.id
            migration.new_instance_type_id = instance.flavor.id
        else:
            migration.old_instance_type_id = instance.instance_type_id
            migration.new_instance_type_id = instance.instance_type_id
        migration.create()

        task = self._build_live_migrate_task(context, instance, destination,
                                             block_migration, disk_over_commit,
                                             migration, request_spec)
        try:
            task.execute()
        except (exception.NoValidHost,
                exception.ComputeHostNotFound,
                exception.ComputeServiceUnavailable,
                exception.InvalidHypervisorType,
                exception.InvalidCPUInfo,
                exception.UnableToMigrateToSelf,
                exception.DestinationHypervisorTooOld,
                exception.InvalidLocalStorage,
                exception.InvalidSharedStorage,
                exception.HypervisorUnavailable,
                exception.InstanceInvalidState,
                exception.MigrationPreCheckError,
                exception.MigrationPreCheckClientException,
                exception.LiveMigrationWithOldNovaNotSupported,
                exception.MigrationSchedulerRPCError) as ex:
            with excutils.save_and_reraise_exception():
                # TODO(johngarbutt) - eventually need instance actions here
                _set_vm_state(context, instance, ex, instance.vm_state)
                migration.status = 'error'
                migration.save()
        except Exception as ex:
            LOG.error(_LE('Migration of instance %(instance_id)s to host'
                          ' %(dest)s unexpectedly failed.'),
                      {'instance_id': instance.uuid, 'dest': destination},
                      exc_info=True)
            _set_vm_state(context, instance, ex, vm_states.ERROR,
                          instance.task_state)
            migration.status = 'error'
            migration.save()
            raise exception.MigrationError(reason=six.text_type(ex))

    def _build_live_migrate_task(self, context, instance, destination,
                                 block_migration, disk_over_commit, migration,
                                 request_spec=None):
        return live_migrate.LiveMigrationTask(context, instance,
                                              destination, block_migration,
                                              disk_over_commit, migration,
                                              self.compute_rpcapi,
                                              self.servicegroup_api,
                                              self.scheduler_client,
                                              request_spec)

    def _build_cold_migrate_task(self, context, instance, flavor,
                                 request_spec, reservations,
                                 clean_shutdown):
        return migrate.MigrationTask(context, instance, flavor,
                                     request_spec,
                                     reservations, clean_shutdown,
                                     self.compute_rpcapi,
                                     self.scheduler_client)

    def _destroy_build_request(self, context, instance):
        # The BuildRequest needs to be stored until the instance is mapped to
        # an instance table. At that point it will never be used again and
        # should be deleted.
        build_request = objects.BuildRequest.get_by_instance_uuid(
            context, instance.uuid)
        # TODO(alaski): Sync API updates of the build_request to the
        # instance before it is destroyed. Right now only locked_by can
        # be updated before this is destroyed.
        build_request.destroy()

    def _populate_instance_mapping(self, context, instance, host):
        try:
            inst_mapping = objects.InstanceMapping.get_by_instance_uuid(
                    context, instance.uuid)
        except exception.InstanceMappingNotFound:
            # NOTE(alaski): If nova-api is up to date this exception should
            # never be hit. But during an upgrade it's possible that an old
            # nova-api didn't create an instance_mapping during this boot
            # request.
            LOG.debug('Instance was not mapped to a cell, likely due '
                      'to an older nova-api service running.',
                      instance=instance)
            return None
        else:
            try:
                host_mapping = objects.HostMapping.get_by_host(context,
                        host['host'])
            except exception.HostMappingNotFound:
                # NOTE(alaski): For now this exception means that a
                # deployment has not migrated to cellsv2 and we should
                # remove the instance_mapping that has been created.
                # Eventually this will indicate a failure to properly map a
                # host to a cell and we may want to reschedule.
                inst_mapping.destroy()
                return None
            else:
                inst_mapping.cell_mapping = host_mapping.cell_mapping
                inst_mapping.save()
        return inst_mapping

    # NOTE(danms): This is never cell-targeted because it is only used for
    # cellsv1 (which does not target cells directly) and n-cpu reschedules
    # (which go to the cell conductor and thus are always cell-specific).
    def build_instances(self, context, instances, image, filter_properties,
            admin_password, injected_files, requested_networks,
            security_groups, block_device_mapping=None, legacy_bdm=True):
        # TODO(ndipanov): Remove block_device_mapping and legacy_bdm in version
        #                 2.0 of the RPC API.
        # TODO(danms): Remove this in version 2.0 of the RPC API
        if (requested_networks and
                not isinstance(requested_networks,
                               objects.NetworkRequestList)):
            requested_networks = objects.NetworkRequestList.from_tuples(
                requested_networks)
        # TODO(melwitt): Remove this in version 2.0 of the RPC API
        flavor = filter_properties.get('instance_type')
        if flavor and not isinstance(flavor, objects.Flavor):
            # Code downstream may expect extra_specs to be populated since it
            # is receiving an object, so lookup the flavor to ensure this.
            flavor = objects.Flavor.get_by_id(context, flavor['id'])
            filter_properties = dict(filter_properties, instance_type=flavor)

        request_spec = {}
        try:
            # check retry policy. Rather ugly use of instances[0]...
            # but if we've exceeded max retries... then we really only
            # have a single instance.
            request_spec = scheduler_utils.build_request_spec(
                context, image, instances)
            scheduler_utils.populate_retry(
                filter_properties, instances[0].uuid)
            instance_uuids = [instance.uuid for instance in instances]
            hosts = self._schedule_instances(
                    context, request_spec, filter_properties, instance_uuids)
        except Exception as exc:
            updates = {'vm_state': vm_states.ERROR, 'task_state': None}
            for instance in instances:
                self._set_vm_state_and_notify(
                    context, instance.uuid, 'build_instances', updates,
                    exc, request_spec)
                try:
                    # If the BuildRequest stays around then instance show/lists
                    # will pull from it rather than the errored instance.
                    self._destroy_build_request(context, instance)
                except exception.BuildRequestNotFound:
                    pass
                self._cleanup_allocated_networks(
                    context, instance, requested_networks)
            return

        for (instance, host) in six.moves.zip(instances, hosts):
            instance.availability_zone = (
                availability_zones.get_host_availability_zone(context,
                                                              host['host']))
            try:
                # NOTE(danms): This saves the az change above, refreshes our
                # instance, and tells us if it has been deleted underneath us
                instance.save()
            except (exception.InstanceNotFound,
                    exception.InstanceInfoCacheNotFound):
                LOG.debug('Instance deleted during build', instance=instance)
                continue
            local_filter_props = copy.deepcopy(filter_properties)
            scheduler_utils.populate_filter_properties(local_filter_props,
                host)
            # The block_device_mapping passed from the api doesn't contain
            # instance specific information
            bdms = objects.BlockDeviceMappingList.get_by_instance_uuid(
                    context, instance.uuid)

            # This is populated in scheduler_utils.populate_retry
            num_attempts = local_filter_props.get('retry',
                                                  {}).get('num_attempts', 1)
            if num_attempts <= 1:
                # If this is a reschedule the instance is already mapped to
                # this cell and the BuildRequest is already deleted so ignore
                # the logic below.
                inst_mapping = self._populate_instance_mapping(context,
                                                               instance,
                                                               host)
                try:
                    self._destroy_build_request(context, instance)
                except exception.BuildRequestNotFound:
                    # This indicates an instance delete has been requested in
                    # the API. Stop the build, cleanup the instance_mapping and
                    # potentially the block_device_mappings
                    # TODO(alaski): Handle block_device_mapping cleanup
                    if inst_mapping:
                        inst_mapping.destroy()
                    return

            self.compute_rpcapi.build_and_run_instance(context,
                    instance=instance, host=host['host'], image=image,
                    request_spec=request_spec,
                    filter_properties=local_filter_props,
                    admin_password=admin_password,
                    injected_files=injected_files,
                    requested_networks=requested_networks,
                    security_groups=security_groups,
                    block_device_mapping=bdms, node=host['nodename'],
                    limits=host['limits'])

    def _schedule_instances(self, context, request_spec, filter_properties,
            instance_uuids=None):
        scheduler_utils.setup_instance_group(context, request_spec,
                                             filter_properties)
        # TODO(sbauza): Hydrate here the object until we modify the
        # scheduler.utils methods to directly use the RequestSpec object
        spec_obj = objects.RequestSpec.from_primitives(
            context, request_spec, filter_properties)
        hosts = self.scheduler_client.select_destinations(context, spec_obj,
                instance_uuids)
        return hosts

    @targets_cell
    def unshelve_instance(self, context, instance, request_spec=None):
        sys_meta = instance.system_metadata

        def safe_image_show(ctx, image_id):
            if image_id:
                return self.image_api.get(ctx, image_id, show_deleted=False)
            else:
                raise exception.ImageNotFound(image_id='')

        if instance.vm_state == vm_states.SHELVED:
            instance.task_state = task_states.POWERING_ON
            instance.save(expected_task_state=task_states.UNSHELVING)
            self.compute_rpcapi.start_instance(context, instance)
        elif instance.vm_state == vm_states.SHELVED_OFFLOADED:
            image = None
            image_id = sys_meta.get('shelved_image_id')
            # No need to check for image if image_id is None as
            # "shelved_image_id" key is not set for volume backed
            # instance during the shelve process
            if image_id:
                with compute_utils.EventReporter(
                    context, 'get_image_info', instance.uuid):
                    try:
                        image = safe_image_show(context, image_id)
                    except exception.ImageNotFound:
                        instance.vm_state = vm_states.ERROR
                        instance.save()

                        reason = _('Unshelve attempted but the image %s '
                                   'cannot be found.') % image_id

                        LOG.error(reason, instance=instance)
                        raise exception.UnshelveException(
                            instance_id=instance.uuid, reason=reason)

            try:
                with compute_utils.EventReporter(context, 'schedule_instances',
                                                 instance.uuid):
                    if not request_spec:
                        # NOTE(sbauza): We were unable to find an original
                        # RequestSpec object - probably because the instance is
                        # old. We need to mock that the old way
                        filter_properties = {}
                        request_spec = scheduler_utils.build_request_spec(
                            context, image, [instance])
                    else:
                        # NOTE(sbauza): Force_hosts/nodes needs to be reset
                        # if we want to make sure that the next destination
                        # is not forced to be the original host
                        request_spec.reset_forced_destinations()
                        # TODO(sbauza): Provide directly the RequestSpec object
                        # when _schedule_instances(),
                        # populate_filter_properties and populate_retry()
                        # accept it
                        filter_properties = request_spec.\
                            to_legacy_filter_properties_dict()
                        request_spec = request_spec.\
                            to_legacy_request_spec_dict()
                    scheduler_utils.populate_retry(filter_properties,
                                                   instance.uuid)
                    hosts = self._schedule_instances(
                            context, request_spec, filter_properties,
                            [instance.uuid])
                    host_state = hosts[0]
                    scheduler_utils.populate_filter_properties(
                            filter_properties, host_state)
                    (host, node) = (host_state['host'], host_state['nodename'])
                    instance.availability_zone = (
                        availability_zones.get_host_availability_zone(
                            context, host))
                    self.compute_rpcapi.unshelve_instance(
                            context, instance, host, image=image,
                            filter_properties=filter_properties, node=node)
            except (exception.NoValidHost,
                    exception.UnsupportedPolicyException):
                instance.task_state = None
                instance.save()
                LOG.warning(_LW("No valid host found for unshelve instance"),
                            instance=instance)
                return
            except Exception:
                with excutils.save_and_reraise_exception():
                    instance.task_state = None
                    instance.save()
                    LOG.error(_LE("Unshelve attempted but an error "
                                  "has occurred"), instance=instance)
        else:
            LOG.error(_LE('Unshelve attempted but vm_state not SHELVED or '
                          'SHELVED_OFFLOADED'), instance=instance)
            instance.vm_state = vm_states.ERROR
            instance.save()
            return

    @targets_cell
    def rebuild_instance(self, context, instance, orig_image_ref, image_ref,
                         injected_files, new_pass, orig_sys_metadata,
                         bdms, recreate, on_shared_storage,
                         preserve_ephemeral=False, host=None,
                         request_spec=None):

        with compute_utils.EventReporter(context, 'rebuild_server',
                                          instance.uuid):
            node = limits = None
            if not host:
                if not request_spec:
                    # NOTE(sbauza): We were unable to find an original
                    # RequestSpec object - probably because the instance is old
                    # We need to mock that the old way
                    filter_properties = {'ignore_hosts': [instance.host]}
                    request_spec = scheduler_utils.build_request_spec(
                            context, image_ref, [instance])
                else:
                    # NOTE(sbauza): Augment the RequestSpec object by excluding
                    # the source host for avoiding the scheduler to pick it
                    request_spec.ignore_hosts = request_spec.ignore_hosts or []
                    request_spec.ignore_hosts.append(instance.host)
                    # NOTE(sbauza): Force_hosts/nodes needs to be reset
                    # if we want to make sure that the next destination
                    # is not forced to be the original host
                    request_spec.reset_forced_destinations()
                    # TODO(sbauza): Provide directly the RequestSpec object
                    # when _schedule_instances() and _set_vm_state_and_notify()
                    # accept it
                    filter_properties = request_spec.\
                        to_legacy_filter_properties_dict()
                    request_spec = request_spec.to_legacy_request_spec_dict()
                try:
                    hosts = self._schedule_instances(
                            context, request_spec, filter_properties,
                            [instance.uuid])
                    host_dict = hosts.pop(0)
                    host, node, limits = (host_dict['host'],
                                          host_dict['nodename'],
                                          host_dict['limits'])
                except exception.NoValidHost as ex:
                    with excutils.save_and_reraise_exception():
                        self._set_vm_state_and_notify(context, instance.uuid,
                                'rebuild_server',
                                {'vm_state': instance.vm_state,
                                 'task_state': None}, ex, request_spec)
                        LOG.warning(_LW("No valid host found for rebuild"),
                                    instance=instance)
                except exception.UnsupportedPolicyException as ex:
                    with excutils.save_and_reraise_exception():
                        self._set_vm_state_and_notify(context, instance.uuid,
                                'rebuild_server',
                                {'vm_state': instance.vm_state,
                                 'task_state': None}, ex, request_spec)
                        LOG.warning(_LW("Server with unsupported policy "
                                        "cannot be rebuilt"),
                                    instance=instance)

            try:
                migration = objects.Migration.get_by_instance_and_status(
                    context, instance.uuid, 'accepted')
            except exception.MigrationNotFoundByStatus:
                LOG.debug("No migration record for the rebuild/evacuate "
                          "request.", instance=instance)
                migration = None

            compute_utils.notify_about_instance_usage(
                self.notifier, context, instance, "rebuild.scheduled")

            instance.availability_zone = (
                availability_zones.get_host_availability_zone(
                    context, host))

            self.compute_rpcapi.rebuild_instance(context,
                    instance=instance,
                    new_pass=new_pass,
                    injected_files=injected_files,
                    image_ref=image_ref,
                    orig_image_ref=orig_image_ref,
                    orig_sys_metadata=orig_sys_metadata,
                    bdms=bdms,
                    recreate=recreate,
                    on_shared_storage=on_shared_storage,
                    preserve_ephemeral=preserve_ephemeral,
                    migration=migration,
                    host=host, node=node, limits=limits)

    # TODO(avolkov): move method to bdm
    @staticmethod
    def _volume_size(instance_type, bdm):
        size = bdm.get('volume_size')
        # NOTE (ndipanov): inherit flavor size only for swap and ephemeral
        if (size is None and bdm.get('source_type') == 'blank' and
                bdm.get('destination_type') == 'local'):
            if bdm.get('guest_format') == 'swap':
                size = instance_type.get('swap', 0)
            else:
                size = instance_type.get('ephemeral_gb', 0)
        return size

    def _create_block_device_mapping(self, cell, instance_type, instance_uuid,
                                     block_device_mapping):
        """Create the BlockDeviceMapping objects in the db.

        This method makes a copy of the list in order to avoid using the same
        id field in case this is called for multiple instances.
        """
        LOG.debug("block_device_mapping %s", list(block_device_mapping),
                  instance_uuid=instance_uuid)
        instance_block_device_mapping = copy.deepcopy(block_device_mapping)
        for bdm in instance_block_device_mapping:
            bdm.volume_size = self._volume_size(instance_type, bdm)
            bdm.instance_uuid = instance_uuid
            with obj_target_cell(bdm, cell):
                bdm.update_or_create()
        return instance_block_device_mapping

    def _bury_in_cell0(self, context, request_spec, exc,
                       build_requests=None, instances=None):
        """Ensure all provided build_requests and instances end up in cell0.

        Cell0 is the fake cell we schedule dead instances to when we can't
        schedule them somewhere real. Requests that don't yet have instances
        will get a new instance, created in cell0. Instances that have not yet
        been created will be created in cell0. All build requests are destroyed
        after we're done. Failure to delete a build request will trigger the
        instance deletion, just like the happy path in
        schedule_and_build_instances() below.
        """
        try:
            cell0 = objects.CellMapping.get_by_uuid(
                context, objects.CellMapping.CELL0_UUID)
        except exception.CellMappingNotFound:
            # Not yet setup for cellsv2. Instances will need to be written
            # to the configured database. This will become a deployment
            # error in Ocata.
            LOG.error(_LE('No cell mapping found for cell0 while '
                          'trying to record scheduling failure. '
                          'Setup is incomplete.'))
            return

        build_requests = build_requests or []
        instances = instances or []
        instances_by_uuid = {inst.uuid: inst for inst in instances}
        for build_request in build_requests:
            if build_request.instance_uuid not in instances_by_uuid:
                # This is an instance object with no matching db entry.
                instance = build_request.get_new_instance(context)
                instances_by_uuid[instance.uuid] = instance

        updates = {'vm_state': vm_states.ERROR, 'task_state': None}
        legacy_spec = request_spec.to_legacy_request_spec_dict()
        for instance in instances_by_uuid.values():
            with obj_target_cell(instance, cell0) as cctxt:
                instance.create()
                # Use the context targeted to cell0 here since the instance is
                # now in cell0.
                self._set_vm_state_and_notify(
                    cctxt, instance.uuid, 'build_instances', updates,
                    exc, legacy_spec)
                try:
                    # We don't need the cell0-targeted context here because the
                    # instance mapping is in the API DB.
                    inst_mapping = \
                        objects.InstanceMapping.get_by_instance_uuid(
                            context, instance.uuid)
                    inst_mapping.cell_mapping = cell0
                    inst_mapping.save()
                except exception.InstanceMappingNotFound:
                    pass

        for build_request in build_requests:
            try:
                build_request.destroy()
            except exception.BuildRequestNotFound:
                # Instance was deleted before we finished scheduling
                inst = instances_by_uuid[build_request.instance_uuid]
                with obj_target_cell(inst, cell0):
                    inst.destroy()

    def schedule_and_build_instances(self, context, build_requests,
                                     request_specs, image,
                                     admin_password, injected_files,
                                     requested_networks, block_device_mapping):
        legacy_spec = request_specs[0].to_legacy_request_spec_dict()
        # Add all the UUIDs for the instances
        instance_uuids = [spec.instance_uuid for spec in request_specs]
        try:
            hosts = self._schedule_instances(context, legacy_spec,
                        request_specs[0].to_legacy_filter_properties_dict(),
                        instance_uuids)
        except Exception as exc:
            LOG.exception(_LE('Failed to schedule instances'))
            self._bury_in_cell0(context, request_specs[0], exc,
                                build_requests=build_requests)
            return

        host_mapping_cache = {}

        for (build_request, request_spec, host) in six.moves.zip(
                build_requests, request_specs, hosts):
            filter_props = request_spec.to_legacy_filter_properties_dict()
            instance = build_request.get_new_instance(context)
            scheduler_utils.populate_retry(filter_props, instance.uuid)
            scheduler_utils.populate_filter_properties(filter_props,
                                                       host)

            # Convert host from the scheduler into a cell record
            if host['host'] not in host_mapping_cache:
                try:
                    host_mapping = objects.HostMapping.get_by_host(
                        context, host['host'])
                    host_mapping_cache[host['host']] = host_mapping
                except exception.HostMappingNotFound as exc:
                    LOG.error(_LE('No host-to-cell mapping found for selected '
                                  'host %(host)s. Setup is incomplete.'),
                              {'host': host['host']})
                    self._bury_in_cell0(context, request_spec, exc,
                                        build_requests=[build_request],
                                        instances=[instance])
                    continue
            else:
                host_mapping = host_mapping_cache[host['host']]

            cell = host_mapping.cell_mapping

            # Before we create the instance, let's make one final check that
            # the build request is still around and wasn't deleted by the user
            # already.
            try:
                objects.BuildRequest.get_by_instance_uuid(
                    context, instance.uuid)
            except exception.BuildRequestNotFound:
                # the build request is gone so we're done for this instance
                LOG.debug('While scheduling instance, the build request '
                          'was already deleted.', instance=instance)
                continue
            else:
                instance.availability_zone = (
                    availability_zones.get_host_availability_zone(
                        context, host['host']))
                with obj_target_cell(instance, cell):
                    instance.create()

            # send a state update notification for the initial create to
            # show it going from non-existent to BUILDING
            notifications.send_update_with_states(context, instance, None,
                    vm_states.BUILDING, None, None, service="conductor")

            with obj_target_cell(instance, cell) as cctxt:
                objects.InstanceAction.action_start(
                    cctxt, instance.uuid, instance_actions.CREATE,
                    want_result=False)
                instance_bdms = self._create_block_device_mapping(
                    cell, instance.flavor, instance.uuid, block_device_mapping)

            # Update mapping for instance. Normally this check is guarded by
            # a try/except but if we're here we know that a newer nova-api
            # handled the build process and would have created the mapping
            inst_mapping = objects.InstanceMapping.get_by_instance_uuid(
                context, instance.uuid)
            inst_mapping.cell_mapping = cell
            inst_mapping.save()

            if not self._delete_build_request(
                    build_request, instance, cell, instance_bdms):
                # The build request was deleted before/during scheduling so
                # the instance is gone and we don't have anything to build for
                # this one.
                continue

            # NOTE(danms): Compute RPC expects security group names or ids
            # not objects, so convert this to a list of names until we can
            # pass the objects.
            legacy_secgroups = [s.identifier
                                for s in request_spec.security_groups]

            with obj_target_cell(instance, cell) as cctxt:
                self.compute_rpcapi.build_and_run_instance(
                    cctxt, instance=instance, image=image,
                    request_spec=request_spec,
                    filter_properties=filter_props,
                    admin_password=admin_password,
                    injected_files=injected_files,
                    requested_networks=requested_networks,
                    security_groups=legacy_secgroups,
                    block_device_mapping=instance_bdms,
                    host=host['host'], node=host['nodename'],
                    limits=host['limits'])

    def _delete_build_request(self, build_request, instance, cell,
                              instance_bdms):
        """Delete a build request after creating the instance in the cell.

        This method handles cleaning up the instance in case the build request
        is already deleted by the time we try to delete it.

        :param build_request: the build request to delete
        :type build_request: nova.objects.BuildRequest
        :param instance: the instance created from the build_request
        :type instance: nova.objects.Instance
        :param cell: the cell in which the instance was created
        :type cell: nova.objects.CellMapping
        :param instance_bdms: list of block device mappings for the instance
        :type instance_bdms: nova.objects.BlockDeviceMappingList
        :returns: True if the build request was successfully deleted, False if
            the build request was already deleted and the instance is now gone.
        """
        try:
            build_request.destroy()
        except exception.BuildRequestNotFound:
            # This indicates an instance deletion request has been
            # processed, and the build should halt here. Clean up the
            # bdm and instance record.
            with obj_target_cell(instance, cell) as cctxt:
                with compute_utils.notify_about_instance_delete(
                        self.notifier, cctxt, instance):
                    try:
                        instance.destroy()
                    except exception.InstanceNotFound:
                        pass
                    except exception.ObjectActionError:
                        # NOTE(melwitt): Instance became scheduled during
                        # the destroy, "host changed". Refresh and re-destroy.
                        try:
                            instance.refresh()
                            instance.destroy()
                        except exception.InstanceNotFound:
                            pass
            for bdm in instance_bdms:
                with obj_target_cell(bdm, cell):
                    try:
                        bdm.destroy()
                    except exception.ObjectActionError:
                        pass
            return False
        return True
